Lasers are being increasingly utilized to treat various dermatological conditions, and in particular to treat and destroy in various ways hair follicles for the removal of unwanted hair, spider veins, leg veins, other veins or blood vessels in the upper portions of the dermis which are visible through the epidermis, lesions, unwanted tattoos and the like. One problem with such laser treatments is that the only way to get the laser energy to the area in the dermis where treatment is desired is to transmit the laser energy to such area through the overlying epidermis. Further, since many of the treatments involve absorption of energy by the melanin in the dermal area being treated, and there is also melanin in the epidermis, particularly in the inner portion thereof, it is not possible to use a wavelength of laser energy for the treatment which will not also be absorbed to some extent in the epidermis. Even when wavelengths are used which are preferentially absorbed by blood or hemoglobin, there is still some absorption of laser energy in the epidermis. Further, the deeper in the dermis that treatment is desired and/or the larger the element being treated, the more laser energy must be used and the longer the pulse duration for such laser energy. This increase in energy applied through the epidermis also results in greater absorption of energy by the epidermis.
Therefore, one limitation on the energies which can be used for various dermatological treatments in the dermis, and in particular on the depths in the dermis at which treatments can be performed, is that the energy cannot be so high as to cause damage to the epidermis. One way around this problem, which is for example discussed in U.S. Pat. Nos. 5,057,104 and 5,282,797, issued Oct. 15, 1991 and Feb. 1, 1994, respectively, to Cyrus Chess (the "Chess patents"), is to either place a cold pack in contact with the skin through which laser energy is passed, or to circulate cooling water through an applicator which is in contact with the epidermis. This permits the epidermis to be cooled so as to reduce or possibly eliminate thermal damage to the epidermis while still permitting laser treatment to be performed in the underlying dermal region.
However, these prior art systems have at least two limitations. The first limitation is that it is desirable to have cooling through the entire epidermal layer, which is typically about 0.1 mm thick, since most of the absorption is in the melanin located in the lower portions of the epidermis. However, it is not desirable that the cooling extend significantly below the depth of the epidermis into the dermal layer, cooling at greater depth potentially inhibiting the desired thermal damage to the element in this region. Since a cold pack loses its ability to cool with time, the pack will normally be too cold initially, cooling to too great a depth and, as the pack heats, may not cool to a sufficient depth. The result may thus be to inhibit the desired dermatological treatment while still permitting thermal damage to the epidermis, an undesirable combination. The circulating water embodiment can provide a more even temperature; however, it is still difficult with the circulating water embodiment to assure that cooling for all individuals being treated is to the desired depth, and it is likely that in most instances, the cooling will either be too deep or not deep enough. These techniques also have other limitations, including being cumbersome and relatively expensive to fabricate and/or to use.
The need to control damage to a patient's epidermis means that laser dermatological procedures must now be performed by physicians or other highly trained individuals, and that great care must be exercised in performing such procedures to assure that epidermal damage does not occur without interfering with the desired treatment. It would therefore be preferable if an automatic procedure could be provided to control epidermal temperature through the full depth of the epidermis in the area being treated so as to protect against epidermal damage to a patient while optimizing treatment, thereby permitting laser dermatology procedures to be performed by less highly trained, and therefore less expensive, personnel. However, because of variations in skin pigmentation, differences in epidermal depth and other dermatological differences among patients, such an automatic procedure is difficult to achieve.
A related, but opposite, problem arises in performing certain skin resurfacing/wrinkle removal procedures where the objective is to heat and destroy only the most surface layer(s) of skin with minimal damage to underlying layers. This requires tight control of factors such as laser energy, pulse duration and repetition rate. Again, variations in patient skin means that the procedure can be safely performed only by highly trained and skilled personnel with little margin for error. Similar problems of achieving desired laser treatment while controlling/limiting damage to tissue outside the treatment region arise for other laser medical procedures.
A need therefore exists for an improved method and apparatus for use particularly with laser dermatology systems which automatically protects the patient against damage in skin areas not under treatment, while not interfering with the laser treatment in the skin areas under treatment, thus making such treatments safer and potentially less painful, and permitting the procedures to be performed by less highly trained, and therefore lower cost, personnel.